Well, in all fairness, DAJ is more like a 'demo', meaning, it's only the first chapter with more to come. As such, imagine the first chapter in most RPGs where you form your party with companions you meet. In most of them, just like in DAJ, at the point chapter 1 ends you haven't met many NPCs, usually your group is made of all the NPCs you've met, no mix-match possible at this point (although in DAJ so far, you have a max of 3 members and there are 3 NPCs plus yourself, so you already have a decision to make)